1. Industrial Field of Utilization
The present invention relates to a fan motor adapted for high speed rotation.
2. Prior Art
For use with a common electric cleaner, there has been provided a fan motor having a rotor shaft rotatably mounted at both end on ball bearings and adapted to have a fan at the one end thereof.
As shown in FIG. 7, the arrangement of such a prior art fan motor 40 indicates a stator 41, a rotor 42, a brush 43, and a commutator 44. The rotor 42 and the commutator 44 are fixedly mounted on the intermediate portion of a rotor shaft 45 which has a fan 46 at one end. The rotor shaft 45 is movably supported by the first ball bearing 47 interposed between the rotor 42 and the fan 46 and the second ball bearing 48 disposed at the other end. The numeral 49 represents an air intake opening and the numeral 50 represents a diffuser.
For movement, the rotor 42 rotates at a high speed when energized from the brush 43 via the commutator 44 and thus, actuates the fan 46 mounted to the end of the rotor shaft 45 so that the air is drawn through the air intake opening 49 and then, exhausted via the diffuser 50.
If the rotation of the motor, which is 20,000 to 30,000 rpm in a conventional electric cleaner, is increased to 50,000 to 60,000 rpm for in order to reduce the size of the device, the problem will arise that there is increased noise and vibration produced by contact between the brush 43 and the commutator 44 and also, from the ball bearings 47 and 48 supporting the rotor shaft 45. The life of such components will thereby be shortened. This may result in a considerable loss of torque and a decline in efficiency.
Although, noise and vibration caused between the brush 43 and the commutator 44, can be solved by using a brushless motor, the noise and vibration caused by ball bearings 47, 48 will remain. Thus, the life of the rotor shaft will be short and the torque loss will be inevitable.